1. Technical Field
The present invention relates to a vehicle lighting device and, more particularly, the technology to improve a pleasant appearance of a vehicle lighting device in which a lens and a housing are joined together by the laser welding, especially an inner area of pleasing appearance when such inner area is looked through a lens.
2. Related Art
The laser welding can carry out surely joint of two members in a short time with good outer appearance. Therefore, such laser welding is suited for the joint between the lens and the housing in the vehicle lighting device.
In the vehicle lighting device, when the lens is joined to the housing by the laser welding, normally the welded portion of the housing is irradiated with the laser beam that is passed through the lens. Then, the welded portion of the housing generates a heat and melts in response to the irradiation of the laser beam, and then such heat is conducted to the welded portion of the lens to melt that portion. Thus, both portions are joined together.
For that purpose, the material such as an acrylic resin (poly(methyl methacrylate)), or the like, which has the good transmittance of the laser beam, is used as the lens, while the material such as ASA (acrylonitrile styrene acrylate), which absorbs the laser beam, is used as the housing.
Meanwhile, if a color of the housing is gray, carbon as the laser absorbent is mixed into the resin material. Therefore, the laser welding can be applied to such housing.
By the way, in the vehicle lighting device, especially the car lighting equipment, normally the pleasant appearance of the welded portion of the housing when such portion is looked through the lens is improved by coloring the housing in a chromatic color in the similar color range to the color of the lens.
However, because no carbon is contained in the resin material of the chromatic color, it is impossible to apply the laser welding as it is. For this reason, it is indispensable to apply previously the laser absorbent to the welded portion of the housing prior to the laser welding. The application of the laser absorbent to the laser welded portion is executed by the method of coating the laser absorbent, pasting the sheet-like laser absorbent, or the like, for example.
The previous application of the laser absorbent to the welded portion of the housing prior to the laser welding increases the steps by one step, and such a problem lies that the workability becomes worse. Also, the method of coating the laser absorbent needs the additional equipment, e.g., care about the work environment, or the like because of the presence of the solvent, and others. Further, the sheet of the laser absorbent is expensive.